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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

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COLUMBIA GLACIER                                          285
cliff and the water also deepens uniformly southward but at the rate of only 98 feet to the mile, the depth 3f miles from the glacier being 426 feet (Fig. 35).
The cross section of the fiord (Fig. 36) is of a very broad U-shape, with broad flat bottom, typical of glacially-sculptured troughs.
There are submerged hanging valleys on each side of the main fiord, the channel east of Heather Island hanging 474 feet above the bottom of Columbia Bay, while the smaller Granite Cove, at the entrance of which the water is only 18 feet deep, hangs 756 feet. There are also hanging valleys above sea level, one about half way between Granite Cove and Columbia Glacier, on the west side of the fiord, hanging 300 feet above the level of the water, which is here nearly 700 feet deep in midchannel. The whole western slope of the fiord is much over-steepened by glacial erosion, having a slope in many places of over 4000 feet to the mile, with sheer precipices in places and with much bare rock. Cirques, hanging valleys, roches moutonnees forms, over-steepened lower slopes, and truncated spurs are also abundant in the mountains on the eastern side of the fiord, but this side has been less sharply eroded than the western. Glacial striae are rarely seen in Columbia Bay, for soil and moss mask most of the rock ledges.
Glacial Deposits. Glacial deposits form no conspicuous features near Columbia Glacier, and there are no submerged deposits suggestive of moraines in the bay. Heather Island
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FIG. 36.   NATURAL SCALE CROSS-SECTION or COLUMBIA BAT SHOWING SUBMHBGHD HANGING VALLBYB.
is a rock hill, thinly veneered with ground moraine. North and east of Heather Island, however, there are extensive mud flats made by deposits from glacial streams, and through these are scattered striated bowlders carried out by icebergs. It is impossible to tell to what extent similar deposits occur in the deeper waters where the heights of submerged hanging valleys may, therefore, be considered as giving only a mim'TniTm measurement of glacial erosion. The lakes in the valleys southeast of Columbia Glacier may be due either to glacial obstructions or to basiling by sculpture of tributary ice tongues. In the marginal lakes immediately adjacent to the ice there are some glacial deposits, among which the outwash plain of sand and gravel built by the stream from the large glacier distributary on the east is conspicuous. It is over a mile in length.
The lowland next the bay, over which the lobate eastern margin of the glacier was beginning to advance in 1910, is the only extensive area of terminal moraine in the region. It is five-eighths of a mile long, an eighth of a mile or less in width, and has the sharp undulating knob-and-basin topography (PL CXH, A) typical of many terminal moraine areas in the United States. There are a score or more of small ponds in the kettles. Most of the area is covered only by grass, but the parts farthest from the glacier have very small strips of mature conifers with dead trunks heaped up along a push moraine at the border of the westernmost clump. As Grant and Higgins have pointed outJ the shrubs on the grassy moraine surface are not over 20 years of age, or thereabouts, but we do not agree
i Grant, U. S. and Biggins, D. F., Glaciers of the Northern Part of Prince William Sound, Bull. Amer. Geog. Soc., Vol. XTTT. 1910, p. 729 and Fig. 8.